DPanswers

IR and Digital Cameras

Table of Contents

1. Introduction
2. Finding a Suitable Camera
3. IR sensitivity
4. Camera Conversion Links

1. Introduction

All sensors used in digital cameras are (to some extent) sensitive to infrared light. This is simple to verify. Standard remote controls uses infrared light to signal the device. Take a TV or DVD remote control, point the remote at your digital camera and push one of the buttons. No visible light can be seen, but if you look at the preview or review of the remote on your camera's LCD screen, you should see the infrared light emitted by the device as a bright spot.

IR-light may cause image defects such as flare, false colours, hot spots and chromatic aberrations. It is not a good thing (in an ordinary photograph) to have the image affected by IR-light. As a measure against these defects, an IR-blocking filter in usually placed in the front of the camera's sensor.

2. Finding a Suitable Camera

The most suitable cameras for ir-photography are those were the ir-blocking filter put in the camera by the manufacturer has been replaced with an ir-pass filter. One the best placed to find such a camera is eBay. Search eBay for an ir-converted camera.

Some camera models can also be used without modification. This may be worth trying if you already own the camera. But results will be inferior to those you get with a modified camera, so don't bother buying an unmodified camera fir ir-photography.

3. IR sensitivity

Depending on the characteristics of the digital sensor, and the efficiency of the IR-blocking filter, the sensitivity of different digital cameras to infrared light vary a great deal. The simple test with a remote described above will not reveal to what extent your camera is able to register infrared light.

A better test of your camera's infrared capabilities would be to borrow or buy a cheap IR-pass filter such as Hoya R72 or Wratten 89B and go out on a bright sunny day to photograph scenes with a lot of green foliage. Or, if you don't have access to a real IR-pass filter, do the test using an unexposed (black) frame of slide film taped in front of the lens. (Slide film has about the same transparency to near-IR light as the Hoya R72, but it is probably not as good, optically speaking.) A look at the resulting images and the histogram should tell you a lot of how capable the camera is in the near infrared part of the spectrum.

Some time ago, I started to collect data about how sensitive the different cameras were to IR-light. My idea was to find a model that was sensitive enough to give good quality infrared images when used handheld. (I ended up buying an Olympus C2020Z, which has served me well.)

Around 2004, IR-blocking filters used in digital cameras started to become much more effective. As a general rule, cameras released after 2004 need to have their IR-blocking filter removed to if you want to use them for infrared photography.

As a result, I've stopped collecting this data. I'll keep the table on-line for some time, as an assistance to those looking for an old, cheap camera that can be used unmodified for infrared photography.

In the table below, you will find a list of camera models and a column labelled Avg. IS. This column gives the average computed IS (Infrared Sensitivity). This is number that is computed just like Exposure Value (EV), but with a filter in front of the sensor that cut off visible light so that only infrared light pass.

The average IS indicates how sensitive the camera is to infrared light. The higher the average IS, the more sensitive the sensor is to infrared light. For comparison, a camera's sensitivity to a scene lit by bright sunlight corresponds to a EV around 15. To find out how less sensitive the camera is to infrared light, you subtract the Avg. IS in the column below from EV 15, and the result is the difference in number of stops.

Example: The Epson 850Z infrared light sensitivity with the Hoya R72 filter is IS 9, so it is about 6 stops (15-9) less sensitive to infrared light than to visible light with this particular filter.

IS 8 corresponds to f/2 at 1/60th of a second at ISO 100. To use a digital camera for handheld infrared photography, I think it should have an IS of 8 or more if its maximum aperture is f/2.0, and 9 or more if its maximum aperture is f/2.8 (YMMV).

A basic problem with digital IR photography is that thermal noise increases and “hot” pixels appear due to the long exposure times involved. This means that EV is not the only thing that determines suitability of a particular sensor. If a less sensitive sensor has better noise characteristics, then it may be give an overall better IR-performance than one with a higher EV number, but worse noise characteristics.

Table

The table below indicates the relative IR-sensitivity of a number of popular digital cameras, with the average EV for each model indicated (some models that share the same sensor is lumped together.

How to read the table: The first column (Camera) list the camera model, the second lists the computed the average infrared sensitivity (Avg. IS) for the camera, and the third the maximum aperture (Max f/) for the particular camera. Then the next six columns list image specific data: The IS for the particular image (IS), the shutter time (T), the aperture (f/), the ISO setting (ISO), the filter(s) used (Fltr.), and finally, in the Link column, the photographers initials, with a a link back to the page with the original image

Methodology: The IS numbers listed in the table are computed from images taken by different photographers, at different times and under different conditions. It would obviously have been better to make comparisons by setting up all the different cameras under identical conditions and make fair and direct measurements. However, I don't have the resources to do such a controlled experiment, and those who have (e.g. DPreview) are not suffiscient interested in ir-photography to include ir-sensitivity in their standardised testing suite. I give priority to images taken under roughly the same conditions, depicting the same subject matter. This means that if possible, I use images taken with a filter with an IR pass point of 720 nm (Wratten 89B or equivalent) depicting a bright sunlit landscape (f/16, 1/250 sec. at ISO 200, equal to EV 15 in the visible spectrum) with plenty of foliage. While these constraints are not suffiscient to eliminate all errors, it is the best I can do. What I eventually hope, is to have a large number of samples from each camera. By computing an average IS I hope that the “law of large numbers” eventually will even things out.

Disclaimer: Many of the samples linked to has been extensively post-processed by skilled artists. Do not assume that this is how the image appears out of the camera. The samples indicate at most what can be expressed by a skilled craftsman or artist and a particular camera, lens and filter combination.

Exposure Value

The exposure value (EV) system was invented in the 1950s to give an absolute measure of expo­sure needed. You get an EV when you combine sensor sensitiv­ity, shutter speed and aperture. Sensor sensitivity settings, shutter speed and aperture combina­tions that results in the same exposure have the same EV (e.g. ISO 100, f/8 and 1/125 have the same EV as ISO 100, f/5.6 and 1/250 and ISO 200, f/8 and 1/250, and so on). EV is designated by integers such as ..., -2, -1, 0, 1, 2, 3, 4, 5, ... . Each increment of 1 EV corresponds to a increase in the light reaching the sensor by a factor of 2 (letting you use half the ISO value, double the shutter speed, or close the aperture down 1 stop).

Formally, at ISO 100, EV 0 corresponds to a shutter speed of 1 second and an aperture of f/1.0:

EV 0 = (ISO 100, f/1.0, 1 second)

EV 0 is very dark, e.g. a night scene with dim ambient light. By comparison EV 15 is f/16 at 1/125th second, at ISO 100 - this is what you would use for a landscape in bright sunlight (aka known as “sunny sixteen”).

See Fred Parker's Ultimate Exposure Computer if you are interested in learning more about EV.

Note: There is some confusion whether EV takes film speed into account or not. Some insists that EV is only valid for ISO 100, and use a different term, such as light value (LV), or actual EV (aEV) for a number that is a function of the film speed, aperture and shutter triplet. To cut a long story short, the most useful metric for digital, where film speed is just as variable as the other two, is one that takes film speed into account, so that is what I use and call EV. Please note that the calculator featured in the excellent glossary at DPreview is in agreement.

4. Camera Conversion Links

The links below leads to some pages outlining DIY procedures for IR camera conversion. I've also included some links to outfits that claim that they will do the conversion for you. Linking to these outfits is not an endorsement. I haven't used any of these companies or individuals, and don't know anything about the quality of their work.

• Canon G-series (Tony Kaplan)
• Canon 450D (Gary Honis)
• Fujifilm FinePix S3 Pro UVIR (DPreview)
• Minolta D7x (Jens Rösner)
• Nikon 950/990 (James Wooten)
• Nikon D40 (PhotoCamel)
• Nikon D50 (Lifepixel)
• Nikon D70 (Astrosurf)
• Olympus Cx0y0 (Jens Rösner)
• Sigma SD10 (Gisle Hannemyr)
• SonyEricsson P910i (Yigit Guler)
• Webcam (Geoff Johnson)
• Webcam (WikiHow)
• David Burren Used to IR-enable many DSLRs + compacts
• Hutec: IR-enables various Fuji and Canons
• Lifepixel: IR-enables Canon, Fuji and Nikon cameras + DIY tutorials and materials
• Maxmax: Sells IR-enabled digital cameras

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